Gas turbine engines with compressor rotor cooling

ABSTRACT

The disclosure shows a system for cooling the rotor of an axial flow compressor incorporated in a gas turbine engine. Air is ducted from the first compressor stage discharge into the interior of the rotor. This cooling air flows to the downstream end of the rotor and is then ducted back into the compressor inlet.

United States Patent Koff [ Mar. 7, 1972 [54] GAS TURBINE ENGINES WITHCOMPRESSOR ROTOR COOLING [72] Inventor: Bernard L. Koff, Cincinnati,Ohio [73] Assignee: General Electric Company [22] Filed: June 1, 1970[21] App1.No.: 41,958

[52] U.S.Cl ..415/115,415/116,415/175, 184/611 [51] Int. Cl ..F0ld 5/14,F03b 11/00, F04d 29/38 [58] Field ofSearch ..415/115, 116, 175, 53;416/96; 60/3966 [56] Relerences Cited UNITED STATES PATENTS 3,453,8257/1969 May et a1. ..60/39.66 X

2,933,238 4/1960 Sta1ker.... 415/115 X 3,031,132 4/1962 Davies...415/115 X 3,123,283 3/1964 Leis ..415/115 2,910,268 10/1959 Davies eta1. ...415/115 2,973,938 3/1961 Alford ..416/96 Primary Examiner-CarltonR. Croyle Assistant Examiner-Richard E. Gluck Attorney-Derek P.Lawrence, E. S. Lee, 111, Lee H. Sachs, Frank L. Neuhauser, Oscar B.Waddell and Joseph B. Forman [5 7] ABSTRACT The disclosure shows asystem for cooling the rotor of an axial flow compressor incorporated ina gas turbine engine. Air is ducted from the first compressor stagedischarge into the interior of the rotor. This cooling air flows to thedownstream end of the rotor and is then ducted back into the compressorinlet.

9 Claims, 4 Drawing Figures GAS TURBINE ENGINES WITH COMPRESSOR ROTORCOOLING The invention described and claimed in the US. Pat. applicationherein resulted from work done under U.S. Government contract FA-SS66-6.The US. Government has an irrevocable, nonexclusive license under saidapplication to practice and have practiced the invention claimed herein,including the unlimited right to sublicense others to practice and havepracticed the claimed invention for any purpose whatsoever.

The present invention relates to improvements in gas turbine enginesand, more particularly, to improved cooling of compressor rotorsemployed in such engines.

The present invention, while not so limited in its broader aspects, isparticularly motivated by the unique requirements of turbojet enginesemployed in the supersonic propulsion of aircraft. When operating atsupersonic flight conditions, air enters the engine inlet and is shockeddown to subsonic velocities. This air is then pressurized by acompressor to support combustion of fuel in the generation of a highenergy hot gas stream. The temperature rise of the air through the inletand the compressor results in extremely high temperatures in thecompressor and at the discharge thereof the temperature levels arecomparable to those of the hot gas or combustion streams of earlier gasturbine engines.

The high-temperature levels of the compressor have a serious effect onobtaining high-performance operation with a lightweight constructionrequisite for aircraft propulsion. The very fact that temperatures areat such high levels markedly reduces the strength of the materials fromwhich the compressor components are fabricated. This is most critical inthe compressor rotor which must rotate at high speeds. Additionally,thermal gradients in the rotor components induce further stresses. Thesefactors all tend to increase the amount of material in the rotor forsufficient strength and thus to increase its weight. These problems arefurther complicated in large diameter engines required to developsufficient thrust for transport aircraft.

Another factor of high-temperature operation is thermal growth. Thegreater the operating temperature, the larger the radial growth of thetips of the blades mounted on the rotor. Because the casing of thecompressor can have a difi'erent thermal growth under certain operatingconditions, it is difficult to obtain the desired minimum clearancebetween the tips of the blades and the surrounding shrouds mounted onthe casing. These problems can be reduced by minimizing the operatingtemperature of the rotor.

A further problem area, not directly related to temperature levels, isthe high hoop stresses generated in the annular bands or spacers of suchrotors. These spacers are loaded in a hoop sense by the centrifugalforces generated by the high-speed rotation of the rotor.

While it has previously been proposed to cool turbine as well ascompressor rotors to alleviate the problems discussed above, such priorproposals are not fully effective, particularly for application tocooling of compressor rotors incorporated in turbojet engines employedin supersonic propulsion.

Accordingly, one object of the invention is to provide improved coolingof compressor rotors with low-pressure air which additionally reducesthe stress levels of the rotor.

Another object of the invention is to accomplish the above ends and inso doing, provide a lightweight rotor, long-life construction consistentwith the requirements of aircraft propulsion engines.

A further object is to provide improved cooling of compressor rotors andin so doing to minimize clearances between the tips of the rotor bladesand the surrounding shrouds mounted on the compressor casings.

The above ends are attained, in accordance with the broader aspects ofthe invention, by a multistage axial flow compressor comprising a casingand a rotor defining the outer and inner bounds respectively of anannular flow path. The casing has vanes disposed in axially spacedcircumferential rows and the rotor has rows of blades projecting betweenthe vane rows. The blades and vanes pressurize air in a progressivefashion as it moves along the flow path. The rotor includes a generallycylindrical shell having thin-walled end section with at least a portionof the blade rows being mounted on the shell. Means are provided fordirecting air from a region of the flow path having a given pressurelevel into the upstream end portion of the shell's interior. Further,means are provided for ducting air from the downstream portion of theshell's interior to and into a region of the flow path having a lowerpressure level than the given pressure level. In this fashion, the rotoris efficiently and effectively cooled while providing a reduced pressurewhich minimizes hoop loadings in the shell.

Additional features of the invention are found in the provision of acylindrical shell which includes axially spaced annular discs projectinginto the interior thereof and relatively thin annular spacers separatingthe discs. The blades are mounted around the peripheries of at leastsome of these discs. The discs in combination with the end sections andeach other respectively form annular chambers. Air directed into themost upstream of these chambers passes sequentially from chamber tochamber to the ducting means.

Another feature of the invention is found in the utilization of acentral tube extending between the end sections of the shell as acomponent of the ducting means for the rotor. The tube has openings intothe most downstream chamber within he shell, means for blocking thedownstream end of the tube and passageway means from the upstream end ofthe tube to the flow path.

Further, the means for directing air into the shell preferably areprovided adjacent the inner bounds of the flow path and extend in aradial direction through the upstream end section of the shell. Impellermeans are desirably provided to direct the air radially inwardly to adiameter approximating that of the adjacent annular disc when such discsare incorporated in the rotor. Further efficiency is obtained byproviding a shroud for the impeller.

More specific features of the invention include the provision of conicalend sections for the rotor shell. A first stage disc may be secured inspaced relationship from the upstream end section by an annular spacer.The further disc would be bladed and form the first rotor stage of thecompressor. The air ducted into the interior of the rotor would bederived from the first stage of compression and then ducted back intothe flow path upstream of the first stage.

The above and other related objects and features of the invention willbe apparent from a reading of the following description of thedisclosure found in the accompanying drawing and the novelty thereofpointed out in the appended claims.

In the drawing:

FIG. 1 is a schematic depiction of a gas turbine engine;

FIG. 2 is an enlarged longitudinal section of the compressor seen inFIG. 1;

FIG. 3 is a longitudinal section of the forward portion of thecompressor seen in FIG. 2, on a further enlarged scale; and

FIG. 4 is a section taken generally on line lV-IV in FIG. 3.

FIG. 1 schematically illustrates a gas turbine engine of the typeemployed for supersonic flight. Air enters an inlet comprising a spikel0 and then is compressed in a multistage axial flow compressor 12. Thiscompressed air supports combustion of fuel in a combustor 14 to generatea hot gas stream. The hot gas stream drives a turbine 16 which in turn,through a shaft 18, powers the rotor 20 of the compressor 12. The energy'level of the hot gas stream may then be augmented by the combustion offurther fuel in an augmenter or afterburner 22. The hot gas stream isthen discharged from a variable area convergent-divergent nozzle 24 toprovide the necessary thrust for supersonic flight. In subsonic flightoperation, the hot gas stream may or may not be augmented in theafterburner and the noule may be adjusted to other than the illustratedconvergent-divergent configuration.

FIG. 2 illustrates the composite fabrication of the rotor 20 in greaterdetail. This rotor comprises a series of discs 26 around the peripheriesof which are mounted blades 28 constituting the several rows or stagesof the compressor rotor. Each disc also has an annular spacer 30 which,with the exception of the first and second stage discs, is connected tothe adjacent upstream disc 26 by bolts 32. The spacers 30 of the firstand second stage discs and the conical portion 34 of a hollow shaft 36have flanges (see also FIG. 3) which are secured together by furtherbolts 32 with the flange of the cone portion 34 sandwiched in themiddle. The last stage disc 26 also has an integral conical flange 38which is secured to the conical portion 40 of the shaft 18 by bolts 32.A disc 42 is interposed between the flange 38 and the conical portion 40to provide greater strength and rigidity for this bolted connection. Thedescribed rotor thus comprises a generally cylindrical shell havingannular discs projecting into its interior and conical end sections withthe first stage disc secured to the upstream end section.

The annular spacers 30 space the rotating blade rows so that stationaryrows of vanes 44, supported by the compressor casing, may be mountedtherebetween. These vanes turn the air in a known fashion to give it aproper angle of attack on the next succeeding blade row. Labyrinth-typeseals 46 are provided between the vane rows and the spacers 30. Atubular duct 48 is secured at one end to the conical portion 34 by bolts50 and supported on the flange 40 by a slip joint 51. A shroudedimpeller 52 (to be described in greater detail below) is secured to theinner surface of the conical rotor portion 34. An end plate 54 closesoff the downstream end of the duct 48.

Referencing FIGS. 3 and 4, it will be seen that a labyrinth seal tooth46 is formed integrally with the cone portion 34. A plurality of radialslots 56 are formed in the flange of conical portion 34 downstream ofthe seal tooth 46. These slots open into a chamber 58 intermediate thefirst stage stator vanes 44 and the second stage rotor blades 28. Theslots 56 are curved at their outer ends in the direction of rotorrotation which is indicated by the arrow A. Thus, first stagepressurized air is directed inwardly along the inner surface of the coneportion 34 by the shrouded impeller 52. The latter includes a pair ofsheet metal cones 58 and 60 which are held in spaced relationship bysheet metal impellers 62 and 64. The outer sheet metal cone 60 extendsto the base of the flange on the second stage disc spacer 30 andadjacent to the duct 48, thus pressurized air is taken into the centerof the hollow rotor 20 to a diameter approximating that of the bore ofthe adjacent disc 26. This pressurized air pressurizes the chamber onthe upstream side of the second stage disc 26 and is forced into thenext succeeding chamber between the adjacent discs 26 of the second andthird stages. As the pressurized air enters this next chamber,centrifugal force tends to displace the air radially outwardly causingit to flow to the spacer 30. As the air flows along this path, itbecomes heated and by reason of being heated has lesser density, so thatit will flow radially inwardly into the next successive chamber betweenthe next successive pair of discs 26. As air enters each of thesechambers, it again is cooler than the air in the chamber and a flow pathis created in the fashion indicated by the arrows in FIG. 2. Afterpassing into the chamber defined by the bolt disc 42 and the coneportion 40, the air then enters holes 66 to flow in an upstreamdirection through the tube 48. The air then is discharged through holes68 in the conical portion 34 of stub shaft 36 to enter a chamber 70defined by the first stage disc and the cone portion 34, as well as astationary front frame 72 which supports the bearing 74 for the stubshaft 36. The air then flows from the chamber 70 back into thecompressor 12 between inlet guide vanes 76 and the first stage rotorblades 28.

The air discharged back into the compressor becomes mixed with theentering inlet air so that it may dissipate the heat that has beenabsorbed before being recirculated into the described cooling system.

The described cooling system is highly effective in maintaining uniformtemperature distributions in the disc 26 of the several compressorstages as well as the disc 42. The flow path through the compressorbecomes increasingly hotter toward its discharge end. The cooling air inthe initial stages of the compressor maintains the temperature of thediscs essentially uniform from the rims thereof which are disposed inthe compressor chamber and their bores within the interior of the rotor.In the latter stages of the compressor, the discs themselves are reducedin temperature to a substantial degree and yet not to a degree whichwould cause an excessive thermal gradient between the interior portionsof the discs and the rim portion. It will also be noted that the forwardflowing air within the duct 48 is at the highest temperature and that ineffect a heat transfer is obtained between the cooling air flowing intothe successive chambers between the discs 26 and the return air throughthe duct 48. This factor is beneficial in reducing the temperature ofthe return air which is to be returned to the compressor system. Inother words, the hotter the air is when it is returned to the compressorsystem, the greater the energy loss involved.

Another factor to be noted is that the interior of the rotor is ventedto a substantially lower pressure than is exerted on the outer surfacesof the spacers 30 for the latter compressor stages in particular. Sincethe rotational force field is radially outwardly, a restraining pressureis created which substantially reduces the stress levels in the spacercomponents, all toward the end of reducing their thickness and weight.The same is true, of course, in that reducing the operating temperatureof the discs 26 increases their strength to enable a lighter weightconstruction.

Various modifications of the described cooling system will occur tothose skilled in the art within the spirit and scope of the presentinventive concepts, which are therefore to be derived solely from thefollowing claims.

Having thus described the invention what is claimed as novel and desiredto be secured by Letters Patent of the United States is:

l. A multistage axial flow compressor comprising:

a casing defining the outer bounds of an annular flow path for air beingpressurized, said casing having vanes disposed in axially spacedcircumferential rows,

a rotor defining the inner bounds of the annular flow path, said rotorhaving blades mounted thereon in axially spaced circumferential rows,said blade rows projecting between said vane rows and cooperatingtherewith to progressively pressurize air in said flow path, said rotorincluding a generally cylindrical shell having thin-walled end sections,with at least a portion of said blades being mounted on said shell, saidgenerally cylindrical shell including axially spaced annular discsprojecting into the interior thereof and, relatively thin annularspacers separating said discs, said blades being mounted around theperipheries of at least some of the discs, said discs in combinationwith said end sections and each other respectively, forming annularchambers,

means for directing air from a region of the flow path having a givenpressure level, into the most upstream of said chambers within theshells interior, and

means for ducting said air from the downstream end portion of the shellsinterior to and into a region of the flow path having a lower pressurelevel than said given level.

2. A multistage axial flow compressor as in claim 1 wherein,

said ducting means comprises a central tube extending between the endsections of said shell, said tube having openings into the mostdownstream chamber within said shell, means for blocking the downstreamend of said tube and passageway means from the upstream end of said tubeto said flow path.

3. A multistage axial flow compressor as in claim 1 wherein,

the directing means include passageways extending generally radiallythrough the upstream end section of said shell at a distance adjacent toinner bounds of said flow path, and

impeller means for directing the air radially inwardly approximately tothe diameter of the bore of they adjacent disc.

4. An axial flow compressor as in claim 4 wherein,

the impeller means are secured to the upstream end section and have ashroud secured thereto in spaced relation from said upstream endsection, and

further wherein the inlet portions of the passageways through theupstream end section are curved in the direction of rotor rotation.

5. A multistage axial flow compressor as in claim 1 wherein,

the end sections of the rotor are conical,

a further disc is secured to and spaced upstream from the upstreamconical end section by an annular spacer and a plurality of blades aremounted around the periphery of said further disc to form the firstrotor stage of the compressor, sealing means are provided between therotor and the vane row downstream of said first rotor stage, and

the air-directing means comprise passageways through said upstream endsection downstream of the named sealing means, and

the ducting means comprises a central tube extending between the endsections of said shell, said tube having openings into the mostdownstream chamber within said shell, means for blocking the downstreamend of said tube and passageway means extending through the upstream endof said tube, through said rotor, to the upstream side of said furtherdisc.

6. A multistage axial flow compressor as in claim 5 wherein,

impeller means are provided for directing air radially inwardly, fromthe passageways through the end section of said shell, approximately tothe diameter of the bore of the adjacent disc.

7. An axial flow compressor as in claim 6 wherein,

the upstream conical end section is formed by a conical portion formedintegrally with a stub shaft and an outer conical portion formedintegrally with said adjacent disc, said conical portions and the spacerof said further disc having radial flanges bolted together with theflange of the inner conical portion between the other two flanges, and

the air-directing passageways are formed in said inner conical portionflange.

8. An axial flow compressor as in claim 7 wherein,

a conical shroud is secured to said impeller means and extends in spacedrelationship from the inner surface of said inner conical portion fromthe outer conical portion flange to a diameter spaced from said tube.

9. A multistage axial flow compressor as in claim 8 wherein,

the entrances to the radial passageways through said inner cone flangeare curved in the direction of rotor rotation, and

wherein the impeller means include a plurality of angularly spacedimpellers extending from said inner cone flange to the inner diameter ofthe shroud cone and a plurality of shorter impellers extending from saidcone flange partially toward said shroud cone inner diameter.

1. A multistage axial flow compressor comprising: a casing defining theouter bounds of an annular flow path for air being pressurized, saidcasing having vanes disposed in axially spacEd circumferential rows, arotor defining the inner bounds of the annular flow path, said rotorhaving blades mounted thereon in axially spaced circumferential rows,said blade rows projecting between said vane rows and cooperatingtherewith to progressively pressurize air in said flow path, said rotorincluding a generally cylindrical shell having thin-walled end sections,with at least a portion of said blades being mounted on said shell, saidgenerally cylindrical shell including axially spaced annular discsprojecting into the interior thereof and, relatively thin annularspacers separating said discs, said blades being mounted around theperipheries of at least some of the discs, said discs in combinationwith said end sections and each other respectively, forming annularchambers, means for directing air from a region of the flow path havinga given pressure level, into the most upstream of said chambers withinthe shell''s interior, and means for ducting said air from thedownstream end portion of the shell''s interior to and into a region ofthe flow path having a lower pressure level than said given level.
 2. Amultistage axial flow compressor as in claim 1 wherein, said ductingmeans comprises a central tube extending between the end sections ofsaid shell, said tube having openings into the most downstream chamberwithin said shell, means for blocking the downstream end of said tubeand passageway means from the upstream end of said tube to said flowpath.
 3. A multistage axial flow compressor as in claim 1 wherein, thedirecting means include passageways extending generally radially throughthe upstream end section of said shell at a distance adjacent to innerbounds of said flow path, and impeller means for directing the airradially inwardly approximately to the diameter of the bore of theadjacent disc.
 4. An axial flow compressor as in claim 4 wherein, theimpeller means are secured to the upstream end section and have a shroudsecured thereto in spaced relation from said upstream end section, andfurther wherein the inlet portions of the passageways through theupstream end section are curved in the direction of rotor rotation.
 5. Amultistage axial flow compressor as in claim 1 wherein, the end sectionsof the rotor are conical, a further disc is secured to and spacedupstream from the upstream conical end section by an annular spacer anda plurality of blades are mounted around the periphery of said furtherdisc to form the first rotor stage of the compressor, sealing means areprovided between the rotor and the vane row downstream of said firstrotor stage, and the air-directing means comprise passageways throughsaid upstream end section downstream of the named sealing means, and theducting means comprises a central tube extending between the endsections of said shell, said tube having openings into the mostdownstream chamber within said shell, means for blocking the downstreamend of said tube and passageway means extending through the upstream endof said tube, through said rotor, to the upstream side of said furtherdisc.
 6. A multistage axial flow compressor as in claim 5 wherein,impeller means are provided for directing air radially inwardly, fromthe passageways through the end section of said shell, approximately tothe diameter of the bore of the adjacent disc.
 7. An axial flowcompressor as in claim 6 wherein, the upstream conical end section isformed by a conical portion formed integrally with a stub shaft and anouter conical portion formed integrally with said adjacent disc, saidconical portions and the spacer of said further disc having radialflanges bolted together with the flange of the inner conical portionbetween the other two flanges, and the air-directing passageways areformed in said inner conical portion flange.
 8. An axial flow compressoras in claim 7 wherein, a conical shroud is secured to said impellermeans and extends in spaced relationship from the inner surface of saidinner conical portion from the outer conical portion flange to adiameter spaced from said tube.
 9. A multistage axial flow compressor asin claim 8 wherein, the entrances to the radial passageways through saidinner cone flange are curved in the direction of rotor rotation, andwherein the impeller means include a plurality of angularly spacedimpellers extending from said inner cone flange to the inner diameter ofthe shroud cone and a plurality of shorter impellers extending from saidcone flange partially toward said shroud cone inner diameter.